Cannot define multiple columns within the same table that have the same relationship to another table

[graysonhead]

Hey there, currently migrating one of my projects over from Diesel to take advantage of tokio and I'm running into a problem with one of my tables.

Here is the table in question:

(Irrelevant columns omitted for brevity)

CREATE TABLE attackers (
    attacker_id BIGINT unsigned PRIMARY KEY UNIQUE NOT NULL AUTO_INCREMENT,
    ship_type_id BIGINT unsigned,
    weapon_type_id BIGINT unsigned,
    FOREIGN KEY (ship_type_id) REFERENCES esi_types (type_id),
    FOREIGN KEY (weapon_type_id) REFERENCES esi_types (type_id)
);

The generated attackers.rs entity is generated as so:

#[derive(Copy, Clone, Debug, EnumIter, DeriveRelation)]
pub enum Relation {
    CharacterPublicInfo,
    #[sea_orm(
        belongs_to = "super::esi_types::Entity",
        from = "Column::ShipTypeId",
        to = "super::esi_types::Column::TypeId",
        on_update = "Restrict",
        on_delete = "Restrict"
    )]
    EsiTypes,
    #[sea_orm(
        belongs_to = "super::esi_types::Entity",
        from = "Column::WeaponTypeId",
        to = "super::esi_types::Column::TypeId",
        on_update = "Restrict",
        on_delete = "Restrict"
    )]
    EsiTypes,
}

This looks correct, but EsiTypes is defined twice in the enum which is of course not possible.

As expected, the related implementation for the other table type is also duplicated:

impl Related<super::esi_types::Entity> for Entity {
    fn to() -> RelationDef {
        Relation::EsiTypes.def()
    }
}

impl Related<super::esi_types::Entity> for Entity {
    fn to() -> RelationDef {
        Relation::EsiTypes.def()
    }
}

I dug around in the API docs a bit, but I can't seem to find a way to make this schema work. Is there a mechanism to allow this in sea_orm?

[tyt2y3]

Hi there, welcome!

The codegen is a little dumb now indeed.

Basically, it can't be done with Related, but only the Linked trait. The difference is, a pair of Entity can have multiple links, but only one relation.

sea-orm/src/tests_cfg/entity_linked.rs

Lines 4 to 17 in a6dfb41

	pub struct CakeToFilling;
	impl Linked for CakeToFilling {
	type FromEntity = super::cake::Entity;
	type ToEntity = super::filling::Entity;
	fn link(&self) -> Vec<RelationDef> {
	vec![
	super::cake_filling::Relation::Cake.def().rev(),
	super::cake_filling::Relation::Filling.def(),
	]
	}
	}

sea-orm/src/query/join.rs

Lines 286 to 301 in a6dfb41

	fn join_12() {
	assert_eq!(
	cake::Entity::find()
	.find_also_linked(entity_linked::CakeToFilling)
	.build(DbBackend::MySql)
	.to_string(),
	[
	r#"SELECT `cake`.`id` AS `A_id`, `cake`.`name` AS `A_name`,"#,
	r#"`filling`.`id` AS `B_id`, `filling`.`name` AS `B_name`, `filling`.`vendor_id` AS `B_vendor_id`"#,
	r#"FROM `cake`"#,
	r#"LEFT JOIN `cake_filling` ON `cake`.`id` = `cake_filling`.`cake_id`"#,
	r#"LEFT JOIN `filling` ON `cake_filling`.`filling_id` = `filling`.`id`"#,
	]
	.join(" ")
	);
	}

See also #89.

Oh btw, is that a Battleship game?

[tyt2y3]

Did that help?

[graysonhead]

Sorry for the delayed reply, been a bit busy lately to work on side projects. It looks like exactly what I'm looking for, and I'll give it a shot once I get a chance to work on this (hopefully in the next few days.)

Its a PVP statistics tracking system for the MMO Eve online.

Thanks for the help!

[penso]

@tyt2y3 I think you should make it bold and very clear somewhere in the documentation: The difference is, a pair of Entity can have multiple links, but only one relation.

[cryptomeemaw]

sorry any examples of how this was done, i have a situation where i have 2 columns in one table with a relationship to another, unsure how i define the relationship/link in this case also how would i define which column it is on